1. intervening period of time: a period of time between one event and the next
2. intervening distance: the distance between one thing and another
3. U.K. theater Same as intermission (sense 1)
4. music difference in musical pitch: the musical distance between the pitches of two notes
5. mathematics all numbers between two numbers: a set containing all the real numbers or points between two real numbers or points, which are called the endpoints. If the set includes the endpoints it is a closed interval, and if it excludes the endpoints it is an open interval.
[14th century. Via French< Latin intervallum "space between ramparts" < vallum "rampart"]